Certain known radar signal processors contain a clutter canceller and a digital, fast automatic gain control (AGC) in line prior to the fast Fourier transform (FFT) circuit. The clutter canceller is a very narrow band reject filter which eliminates the clutter return from the mainbeam of the radar. The fast AGC limits the signal amplitude in the clutter canceller bandpass so that an FFT of modest dynamic range (such as on the order of 42 dB, for example) may be utilized. Flight experience has demonstrated, however, that the clutter canceller transient response and the AGC action cause a performance loss in high clutter conditions.
The use of full dynamic range FFT processing in a radar signal processor is therefore desirable, as it allows the elimination of both the clutter canceller and the fast AGC. However, utilization of a full dynamic range FFT in the presence of peak clutter requires heavy time domain weighting such that the sidelobes are down greater than 100 dB. Furthermore, known techniques of heavy weighting can cause a loss in target detectability of up to 2 dB and a 50 percent loss in doppler resolution.